This invention relates to apparatus for measuring torque. More particularly, it involves apparatus for sensing the amount of previously applied torque to a fastener.
In a variety of manufacturing applications, it is imperative that the correct amount of torque be applied to a fastener. For example, in automotive applications, it is necessary to make sure that bolts have been tightened within a certain prescribed range of torque in order to properly fasten two parts together. It has been common procedure for a member of the quality control department to use a hand torque wrench to approximate the prior torque level by viewing the movement of the torque indicator just prior to the "give" or breakaway of the fastener. Later improvements of such a test included the use of a wrench which would maintain the position of the indicator at the maximum torque experienced.
Unfortunately, these prior art methods of sensing the applied torque were not very precise and not capable of being accurately reproduced from operator to operator. Even under ideal conditions the torque sensed was the "breakaway" torque which caused further relative movement of the fastener and not the torque delivered to the fastener in the first instance. Under true operating conditions even this breakaway torque could not be accurately sensed because the operator was not capable of instantaneously stopping the level of applied torque as soon as he noticed the fastener motion.
The above-identified parent application provides apparatus for detecting a negative valley in the torque signal which occurs in most fasteners after "breakaway".
A negative peak detector is energized by a switching network upon detection of a negatively sloped signal from the transducer. A display device is utilized to provide a visual indication of the output of the negative peak detector thereby providing a measurement which is closely associated with the amount of torque originally applied to the fastener.
Unfortunately, in some instances the torque signal does not provide a well defined negative valley. The reason for this phenomena is not completely understood but it is believed to be due to the fact that some fasteners have polished threads or are lubricated to such a degree that the torque signal does not always possess a negative slope after breakaway. Operator error in improperly applying the torque to the fastener may also be a cause.
The present invention is directed to solving one or more of these problems.